Tag: CET

The early April warmth was cancelled out a little by the late cold spell in Central England, which although lasted no more than 5 days, did manage to limit the mean temperature to just 8.9°C for the month. The final mean anomaly, which had been running at almost +3°C earlier in the month, ended up at +0.97°C. It was the warmth of the days that help produce the +0.97°C anomaly, the mean maximum anomaly was +1.57°C, whilst the mean minimum anomaly was only +0.39°C. Eleven of the last 12 months have been warmer than average. I still calculate all my anomalies with respect to the 1961-1990 long-term average.

Figure 1 – Data courtesy of the Met Office

One notable extreme maximum record was set during the month on Sunday the 9th, which had a maximum of 21.4°C which was +10.5°C above the average for that day.

The Met Office beat me to a story about extreme Easters of the past, but undaunted, and without the masses of climate data they have at their disposal, I pressed on with a bit of research of my own.

Because Easter is not at a fixed time each year it’s difficult to compare one with another. Easter Sunday can fall as early as the 22nd of March or as late as the 25th of April. I’ve used the daily CET series from 1772 (now there’s a surprise), and calculated a five-day mean, from Maundy Thursday to Bank Holiday Monday to do my comparison with. Because of the time range that easter can fall, I have base it on mean temperature anomalies rather than the mean temperature. So from what I’ve found the coldest Easter period since 1772 occurred in 1892 (fig 3). The Easter Sunday that year fell on the 17th of April so it was by no means early.

Figure 2 – Data courtesy of the Met Office

The mean temperature for the five days between Maundy Thursday and the Bank Holiday Monday in 1892 was 2.1°C, which was -6.4°C below the long-term average for that period (fig 3). The weather chart for the Sunday (fig 1) shows just what a bleak and cold Easter that must have been in eastern parts.

Figure 3 – Data courtesy of the Met Office

I couldn’t resist including the Monthly Weather Report for April 1892 after using it to check out my story because I was taken with some of the phrases that were used by whoever wrote the report. I have highlighted some of them from the PDF that I accessed courtesy of the Met Office (fig 4). The remark about Vapour Tension exceeding 0.25 on the south coast of Ireland and England was a real charmer, I bet sixpence was a lot of money in 1892, and what happened to the Weekly Weather Report?

Conversely, the warmest Easter using the same method, fell in 1926 in Central England at any rate. Easter Sunday that year fell on April 4th, and the five-day mean was +6.5°C above today’s long-term average, and if you look at the synoptic situation (fig 5) you can understand why. I did look for any weather related news for Easter 1926, and mistakenly thought that this was the year of the Easter Rebellion in Ireland, but I was 10 years too late, that occurred in 1916.

The Met Office finally got there act together today, and fixed their web service and updated their CET web page with the latest data. As expected, March 2017 was a very mild month, and when the temperatures were finally confirmed today, it turned out that it had been the 3rd mildest since the monthly series started in 1659. I make the mean temperature for the month 8.68°C, which was exactly 3°C above the 1961-1990 long-term average. It couldn’t quite beat the CET of either March 1938 or 1957, so it ended up being the warmest March since 2012.

Figure 2 – Data courtesy of the Met Office

The month saw four new high minimum temperature records set and one highest maximum record on the 30th.

With my tried and trusted ‘First day of Spring’ algorithm, I estimate that Spring 2017 will be around eight days early in 2017, probably occurring on the 13th of March in Central England (fig 1). As usual I estimate it by calculating the degree days from the Winter solstice, and fix the first day of Spring when that count exceeds the mean number of degrees days between Winter Solstice and the Vernal equinox (December 21st and March 20th). And yes, I do know the time of both these can vary by day or so each year. The estimate is based on using the long-term average temperature for future temperatures, so if it’s warmer than usual in the next couple of weeks it may come even sooner, or later if the next six weeks or so are colder than average. That makes this Spring just over three weeks later than it was last year.

Figure 1

Cold Winters mean cold springs, so the Spring of 1963, the third latest since 1772, didn’t happen till the 4th of May that year, likewise a very mild Winter means a very early Spring as in 1989 , the earliest Spring since 1772, which occurred on St Hilary’s day of that year (fig 1). Of course, Central England has warmed since 1772, and the first day of Spring is occurring much earlier, in fact I estimate that Spring is now 20 days earlier than it was in 1772.

A bit of a late look back at the CET values for January 2017, which was not a particular exciting month in Central England, with a mean temperature of 3.95°C, and mean anomaly that was +0.13°C higher than the 1961-1990 long-term average. Although the first half of the month was very mild, a cold anticyclonic spell from the 18th to the 30th, brought the mean temperature for the month back closer to average. Because the Central England region lies further north than the southeast of England, it escaped the worst of the frosts that occurred there. Just five of the last twenty January’s have been colder than average.

If there are any Guardian comment readers still here at this point, I must confess that I did screw up with the comment saying that the January CET value was wrong, it was correct, well I may have rounded it down to 3.9°C, but it wasn’t the 4.45°C that I said it was but actually 3.95°C. I hadn’t downloaded the latest verified daily values for the month, and so the value that I calculated was still based on the estimates from the Met Office. The reason why I say the January value is +0.13°C above average and the article in the Guardian says it’s -0.2°C below the average, is that I used the 1861-1990 long-term average and the article quotes the 1981-2010 long-term average.

I’m still sticking to my guns about the other comments I made about the January sunshine though, but as I said the statistics used to produce the graphic may well have been calculated from individual station rather than gridded data. If you want to download the data and work out your own anomalies please feel free to do so.

Figure 4 – Data courtesy of the Met Office

I can’t add to the comment (or delete it for that matter) so this will have to suffice as an apology for the moment.

Autumn 2016 in Central England was slightly warmer than average with a mean temperature of 8.57°C (based on provisional figures), which was +0.42°C above the 1961-1990 long-term average. There were a couple of highlights during the Autumn 2016.

A cold spell during the first two weeks of November with a minimum anomaly of -7.2°C on the 8th.

A mild December from the 6th, and exceptionally so during the second week, with two new extreme records broken, marked on the above graph with a red star for a new highest maximum on the 9th, and a blue diamond for a new highest minimum on the 10th.

Six air frost’s so far this Autumn, which may not sound a lot but it’s not far of the average, and certainly higher that in 2013/14.

Yes, a rather cold November 2016, but not exceptionally so in CET series, with a mean temperature for the month of 5.5°C, which was -1.0°C below the 1961-1990 long-term average and in the 36th percentile in the monthly series that started in 1659. That mean anomaly 0f -1.0°C made it the coldest November since 2010 (not much of a headline I know, but I challenge the Met Office Press office to make any more of it than that) and only the second month out of the eleven this year with a negative anomaly, the other month being April. Interestingly the minimum anomaly of -1.34°C was much lower than the maximum anomaly of +0.68°C, reflecting the predominantly anticyclonic nature of the month and the cold nights. Thanks, as always, to the Met Office for the data, and to Gordon Manley for dreaming the whole thing up in the first place.

It’s the last day of what people are now calling ‘meteorological’ autumn, so I thought I would put some code together to display daily Central England Temperature [CET] series for any season as a grid of weekly deciles, along with the corresponding mean temperature and anomaly. I did this so that I could take a closer look at winters in the series since 1772, and rather surprisingly I found no winter has been consistently cold throughout the 13 weekly temperatures deciles (1), although the winter of 1794-95 did come close with 12 out of 13 decile 1 weeks. Another surprise, was that the winter of 1978-79 tied with both 1946-47 and 1962-63 with 10 weeks of decile 1 mean temperatures. One thing that I always seem to be being reminded of is how late the winter of 1946-47 started, and if you look closely the first fours weeks of the winter were indeed average or mild. The code for this has been more than a little awkward to get right, mainly because I’ve added functionality to allow for meteorological seasons and also output the results as quintiles as well as deciles.

It’s seems a long time since the last cold winter in 2009-10, and the weekly deciles since the late 1980’s have been predominantly of the mild 3 variety. The mildest winter that I can see from my results looks to be 1989-90 with 12 weeks of decile 3, followed by 2013-14 with 10 weeks of decile 3, in fact 9 out of the top 10 mildest (astronomical) winters as far as I can see have occurred in the last 30 years if you rank winters by their weekly mean temperature deciles.

I think the best way to visualise Central England Temperatures [CET] is by means (excuse the pun) of a 365 day moving average. Any shorter and it’s a little too ‘noisy’, any longer and you lose some of the more subtle nuances that are present in the underlying daily values. Here is a chart of the last 30 years, spanning the period from November 1986 to November 2016. I have annotated the graph to remind both you and me of what month or season probably caused the various upturns and downturns in the anomalies during those thirty years. At the moment we look like we are possibly at the start of a downturn on the roller coaster ride that the CET series is on, and who knows where that will lead in the coming months.

Data courtesy of the Met Office

By the way, the series in the graph with a black line is a moving 365 day average of a 365 day average and that’s why the line is so smooth. It does take a bit of thinking about, but it seems to work just fine!

The Central England Temperatures [CET] for October 2016 ended up with a bit of a flourish, and what looked liked being a very average month in terms of temperature, ended up a little bit on the warm side. The monthly mean was 11.05°C, which made it +0.54°C above the 1961-1990 long-term average, and the 36th warmest October since 1659 in Central England. I have got egg on my face with this month ending up warmer than average, because I was convinced when it started that it was going to be a cold month in general – my advice to anyone who is reading this is – never trust an analog.

There have been many warm October’s since the 1950’s and this is just one more of them. October is quietly becoming less of an autumn month as the years go by and more of a summer one.

As you can see in the chart below the last week of October was not only warm by day, it was even warmer by night, which pushed the overall mean temperature up that bit higher.